The lack of scientific attention devoted to the placebo effect as a phenomenon in its own right probably reflects the paucity of theoretical positions within which to organize the existing data and design new research. The proposed research is an attempt to advance from a descriptive to an experimental analysis of the placebo effect as a reflection of learning processes and examine the clinical implications of such an analysis in the case of an autoimmune disease. As such, this research addresses the clinical significance of behavior- immune system interactions. Conditioning is an inherent component of most pharmacotherapeutic regimens. The proposed research will capitalize on conditioned immunosuppressive responses to reduce the cumulative amount of corticosteroid medication used in the treatment of psoriasis. Patients would continue to be treated with steroid, but experimental patients would be shifted from their current schedule of continuous reinforcement (active drug whenever medication was applied) to a partial schedule of reinforcement (active drug a percentage of the time and placebo alone at other times). To equate amount of medication, other patients would be treated with a (reduced) dose of steroid in a standard (continuous schedule of reinforcement) treatment regimen. It is hypothesized that, holding cumulative dose constant, a partial schedule of reinforcement will enable patients to be maintained on lower cumulative amounts of corticosteriod than patients treated under a continuous schedule of active drug. Psoriasis is an especially appropriate model in which to evaluate the therapeutic affect of partial schedules of pharmacologic reinforcement which could decrease the amount of drug required to reduce psoriatic plaques and the deleterious "side" effects of long-term steroid treatment. Thus, it may be possible to increase the benefit: risk ratio of drug therapy and, at the same time, reduce the costs of medication. The proposed research is not an attempt to offer a behavioral alternative to drug treatment; it is an attempt to add a behavioral dimension to the design of drug treatment protocols. This is the first attempt to adopt conditioning principles and use schedules of reinforcement to design regimens of drug therapy. If proven effective, this new approach to pharmacotherapy and placebo effects is likely to stimulate new interdisciplinary research in neuropharmacology and behavioral pharmacology for the treatment of autoimmune and a variety of other chronic diseases.